Cantilever probes for nanoscale magnetic and atomic force microscopy

ABSTRACT

The various embodiments discloses a cantilever probe comprising a first electrode and a second electrode engaged to a substrate and a branched cantilever wherein the cantilever comprises a nanostruture. Furthermore, the probe comprises a first arm of the cantilever engaged to the first electrode and a second arm of the cantilever engaged to the second electrode. Additionally, the cantilever probe comprises an electrical circuit coupled to the cantilever wherein the electrical circuit is capable of measuring a change in piezoresistance of the cantilever resulting from an atomic force and/or a magnetic force applied to the cantilever. Additionally, the invention discloses a method of performing atomic force microscopy, magnetic force microscopy, or magnetic resonance force microscopy. The nanostructures may comprise carbon or non-carbon materials. Additionally, the nanostructures may include nanotubes, nanowire, nanofibers and various other types of nanostructures.

RELATED APPLICATION

This application is a continuation-in-part of U.S. application Ser. No.10/665,800, filed on Sep. 18, 2003, which claims the benefit of U.S.Provisional Application No. 60/412,319, filed on Sep. 20, 2002. Theentire teachings of the above applications are incorporated herein byreference.

GOVERNMENT SUPPORT

The present invention was made with partial support from The NationalScience Foundation Grant Number 0210533. The United States Governmentretains certain rights to the invention.

FIELD OF THE INVENTION

The various embodiments disclosed herein relate to micro-dimensionalanalytical probes for Magnetic Force Microscopy, Magnetic ResonanceForce Microscopy and other forms of scanned probe microscopy, includingAtomic Force Microscopy. In particular, the embodiments relate tonanoscale materials having piezoelectric properties such as nanotubes ornanowires with pre-determined morphology that function as analyticalprobes in a Magnetic Force Microscopy, Magnetic Resonance ForceMicroscopy, or Atomic Force Microscopy device or in various otherscanned probe microscopy applications.

BACKGROUND OF THE INVENTION

Magnetic Force Microscopy (hereinafter referred to as MFM) and MagneticResonance Force Microscopy (hereinafter referred to as MRFM) providemicrometer-scale imaging of magnetic structures and surfaces. In MFM, aferromagnet-tipped cantilever is brought into close proximity with asample surface to detect the force between the tip and the sample. Thetip is scanned over the surface to reveal the magnetic domain structureof the sample. A typical application of MFM is in data storagetechnology, such as magnetic disk drives. MRFM is potentiallysignificantly more sensitive than MFM, with capability of providingnanometer-scale three-dimensional (3D) imaging of small structures suchas semiconductor quantum dots (e.g., for quantum computing) andbiological samples such as cells, proteins and DNA.

MRFM is a combination of Nuclear Magnetic Resonance Imaging (MRI) andAtomic Force Microscopy (AFM). A Magnetic Resonance Force Microscope(MRFM) is a microscopic imaging instrument that mechanically detectsmagnetic resonance signals by measuring the force between a permanentmagnet and spin magnetization. Conventional MRI is able to provideimages of muscular tissue, for example, by measuring changes to avoltage induced in a coil inductor when the magnetic spins of the atomsin the tissue are excited by a radio frequency (RF) magnetic field. TheRF field is driven at the natural or “resonance” frequency of the spins,causing them to rotate or precess about a strong static magnetic field.The spins in the case of human MRI studies are those of the hydrogennuclei (protons) in the fat and water in the body (the human body isabout ⅔ hydrogen). The imaging occurs when a gradient, or spatiallyvarying static field is used, such that only a small slice of thespecimen is in resonance with the RF field at any given time. Theposition of this slice is often controllably varied, yielding aposition-sensitive measurement of the resonant spin domain (an MRIimage). Thus, MRI is based on the absorption and emission of energy inthe radio frequency range of the electromagnetic spectrum. The spatialresolution of MRI is about 0.1 millimeter (mm) or perhaps slightly less(10 μm resolution has been achieved in a lab based non-commercial NMRmicroscope).

AFM is fashioned after the scanning tunneling microscope (STM). AFM hasthe capability of imaging individual atoms on the surface of a materialby measuring the atomic-scale repulsive force between the atomsthemselves and the tip of a compliant cantilever, usually made ofsilicon or silicon-nitride. When brought extremely close to the surfaceunder study (on order of about 1 nanometer), the interaction forcesbetween the surface and tip cause the cantilever to deflect or bend.This deflection is then measured, usually by reflecting a laser beam offthe back of the cantilever and toward a photodiode detector. The AFM canaccurately image structures down to the Angstrom scale (10⁻¹⁰ m), abouta million times smaller than that of MRI.

Both an MFM and an MRFM device typically comprise a small ferromagnetthat is attached to the terminal end of an AFM cantilever. Thisferromagnet generates an inhomogeneous magnetic field (a gradientfield), whereby the magnetic field of the ferromagnet decreases sharplywith increasing distance from the cantilever. When a magnetic moment Mis exposed to a gradient magnetic field (δB/δr), it experiences a forceF equal to the product of the moment and the gradient (F=M δB/δr). Ifthe AFM cantilever with the associated magnetic tip is positioned nearthe surface of a specimen material containing a plurality of magneticmoments (spins), the possibility exists for those spins to feel themagnetic gradient δB/δr and thereby the force F. This in turn causes thecantilever to feel an equal and oppositely directed force, causing it todeflect. Thus, the cantilever senses the presence of magnetic spins atand, in the case of MRFM, even beneath the specimen surface.

The relative positions of the cantilever and the specimen may bechanged, or scanned, in an MFM or MRFM device, to yield a spatial map ofthe force F experienced by the cantilever, which translates as a spatialmap of the underlying magnetic spin structure of the specimen. Inaddition to lateral and vertical scanning typical of an AFM device,which provides a topographic map of the surface of a specimen, an MRFMdevice provides additional vertical scan information, resulting inthree-dimensional imaging of the specimen with sub-surface capabilitysimilar to MRI, but with AFM-scale resolution.

The ultimate spatial and magnetic moment resolutions of both the MFMdevice and the MRFM device are determined by the magnitude of themagnetic field gradient δB/δr, the mechanical limitations of thecantilever, and the sensitivity of the cantilever motion detector.Smaller physical dimensions of the cantilever are highly desirable toenable imaging of smaller particles such as cells and proteins and DNA.However, the present state of the art detection scheme employs laserlight directed at and reflected off the backside of the cantilever,toward a photodetector or interferometer. As the cantilever sizedecreases, optical detection becomes increasingly difficult, especiallywhen the cantilever dimensions approach or become less than thewavelength of the light in the detector beam. The use of micro-scalecantilevers is a major factor in limiting MFM and especially MRFMresolution in present devices, which is presently at the 10,000 to100,000 spin level. Micro-dimensional probes that are capable ofdetecting single proton and single electron spin are therefore, notpossible using present cantilevers.

As such, there remains a need in the art for nanoscale cantilevers whichmay be incorporated into such applications as MFM, MRFM, AFM and otherforms of scanned probe microscopy.

SUMMARY OF THE INVENTION

In an embodiment, the disclosure provides an MFM or MRFM analyticaldevice comprising a micro-dimensional probe that is capable of detectingsingle proton and single electron spin. In an embodiment, the disclosurecomprises an MFM or MRFM device comprising a micro-dimensional probe,that is capable of detecting magnetic structures of objects of size onthe order of about one nanometer. An embodiment providesmicro-dimensional cantilever piezoelectric probes for an MFM or MRFMdevice. An embodiment provides a micro-dimensional probe for an MFM orMRFM device that comprises a cantilever composed of a carbon nanotube(herein after referred to as CNT cantilever) that comprises a nanoscaleferromagnetic material or “nanomagnet”. In an embodiment, a cantilevercomprises a nanostruture wherein the nanostructure comprises non-carbonmaterials. In an embodiment, the nanostructure is a nanowire. In anembodiment, the CNT cantilever may be attached to an electrode as acomponent of a microscopic probe which, in turn, is coupled with anelectrical circuit as a component of a device for nanoscale MFM or MRFMmicro-dimensional probes. The device, comprising the probe andelectrical circuit, can be incorporated into an existing scanning probemicroscope (hereinafter referred to as SPM) apparatus havingaccommodation for electrical readout.

In an embodiment, the cantilever comprises a carbon nanotube. Carbonnanotubes (hereinafter referred to as CNTs) offer significant advantagesin that they possess piezoelectric properties. Various materials whichpossess these piezoelectric properties (either intrinsically orextrinsically, explained below) are within the spirit and scope of thepresent invention. The piezoelectric properties allow a means ofinternally detecting the movement of a cantilever comprised of a CNT.The internal detection method eliminates the need for an externaldetection method such as the reflection of a laser beam off thecantilever toward a photodiode detector. CNTs also possess substantiallyhigher strength-to-weight ratio and superior mechanical properties overother materials such as silicon. CNTs can have linear or non-linearmorphologies. Linear CNTs as defined herein, refers to CNTs that do notcontain any branches originating from the surface of individual CNTtubules along their linear axes. Branched CNTs as defined herein, referto non-linear CNTs with at least one location along the linear tubuleaxis or at the tubule terminal from which one or more tubules originate,including having linear tubule axes that are non-identical to the tubulefrom which they originate. Such points of origination of additionaltubules (branch points) are also referred to herein as “junctions”.Branched CNTs can include, for example, “Y-shaped” CNTs and “V-shaped”CNTs. In an embodiment, the cantilever is a Y-shaped CNT. In anembodiment, the cantilever is a V-shaped CNT. Important structuralattributes of CNTs that determine their mechanical and electricalproperties can be controlled and “tailored” for specific proberequirements.

Unlike conventional optical-detection based systems such as MFM andMRFM-based detection wherein the measuring device is scanned byconventional means (for example, those employed by typical scanningprobe microscopes) near a magnetic surface, the cantilever device of theinvention involves the passage of an electric current into and out of(i.e. through) the cantilever, with cantilever tip motion detected via achange in the electrical resistance upon deflection due to thepiezoresistive effect. Conventional resistance bridge circuitry isemployed to measure the resistance and its change due to cantilevermotion. This can be operated in DC (direct current) or AC (alternatingcurrent) modes, using conventional constant current amplitude orconstant voltage amplitude sources. Certain signal-to-noise advantagesare obtained while operating in AC mode, in particular if themeasurement (current/voltage) frequency matches the mechanical resonancefrequency of the cantilever device.

Detection circuitry may include a Wheatstone bridge operated in AC or DCmode, AC phase sensitive detection using a ratio transformer or alock-in detector, or DC detection using a constant current source and asensitive voltmeter. Differential measurements may be employed forincreased sensitivity, by sending an electrical current through twonominally identical piezoresistive sensors in series combination, withonly one of these sensors being in adjacent to the sample surface underinvestigation.

In an embodiment, a method for fabricating an analytical device andmethods for analyzing specimen test samples by nanoscale MFM and bynanoscale MRFM using an analytical device comprising a CNT cantileverprobe is provided. Used for MRFM, the CNT probe enablesthree-dimensional magnetic resonance imaging of samples for detection ofbiological molecules such as DNA, biological cells, and microscopicimperfections such as single impurities in solids, at themolecular/atomic level.

In an embodiment, an MRFM probe is disclosed that includes a CNTcantilever component. In an embodiment, the probe comprises a branchedCNT cantilever, comprising a ferromagnetic material, that is attached toan electrode. In an embodiment, the branched CNT cantilever is attachedto the electrode by at least one of the CNT cantilevers tubules. In anembodiment, the branched CNT cantilever is attached to the electrode bythe ends of the top two arms of the branched CNT cantilever, and thebottom third of the cantilever is extended out from the substrate. In anembodiment, the branch that is extended out from the substrate isreferred to as the cantilevered end. In an embodiment, a ferromagneticmaterial is attached to the terminus of the cantilevered end of the CNTcantilever. In an embodiment, the ferromagnetic material is attached tothe junction of the CNT cantilever. In an embodiment, the cantilevercomprises a terminally capped ferromagnetic layer.

In an embodiment, the ferromagnetic material is a ferromagneticnanoparticle. In an embodiment, the ferromagnetic nanoparticle can actas the MRFM spin probe near a specimen surface.

In an embodiment, an analytical device comprises a probe comprising acarbon nanotube cantilever, having attached thereto a ferromagneticmaterial, coupled to an electrode.

In an embodiment, a method of detection is disclosed for nanoscale MRFMusing a carbon nanotube cantilever. In an embodiment, readout of thecantilever can be achieved electrically, eliminating the need foroptical interferometry or other optical detection methods, which becomeproblematic as cantilever dimensions are reduced tosub-optical-wavelength. In an embodiment, the method uses the intrinsicpiezoelectric or piezoresistance properties of the carbon nanotubes toprovide a readout in the nanoscale MRFM device.

In an embodiment, fabrication and isolation of carbon nanotubecantilevers probes is disclosed. In an embodiment, multi-walled CNTs arepreferred. In an embodiment, the substrate is an electron-beam patternedsubstrate. In an embodiment, the CNT cantilevers can be obtained bygrowing CNTs on a catalyst-containing substrate surface by a number ofknown methods, include chemical vapor deposition. In an embodiment, CNTscan be grown in arrays. In an embodiment, the catalyst containingsurface for CNT growth can be patterned on a material surface byconventional lithography so as to produce CNT “nanocircuits”. In anembodiment, ferromagnetic material can be attached to the terminus ofone of the branches of the cantilever using deposition techniques knownin the art. In an embodiment a cobalt nanorod is attached to thecantilever using a polymeric adhesive.

In an embodiment, the ferromagnetic material is attached to the nanotubeas a result of nanotube formation, that is, a portion of the(ferromagnetic) catalyst material that nucleates CNT groups remainsfixed to the end of the CNT.

Additionally, the fabrication of an electrode comprising CNT cantileverprobes is disclosed. In an embodiment, the CNTs can be attached to theelectrode on a lithographically prepared substrate using SPMmanipulation by standard methods known in the art. In an embodiment, theCNTs comprised in the probes can be formed directly on the substrate.

In an embodiment, a method of constructing an analytical device for usein nanoscale MRFM is disclosed. Additionally, an embodiment comprises amethod of analyzing a sample with nanoscale MRFM.

In an embodiment, a cantilever probe comprises a first electrode and asecond electrode engaged to a substrate and a branched cantileverwherein the cantilever comprises a nanostruture. Furthermore, the probecomprises a first arm of the cantilever engaged to the first electrodeand a second arm of the cantilever engaged to the second electrode.Additionally, the cantilever probe comprises an electrical circuitcoupled to the cantilever wherein the electrical circuit is capable ofmeasuring a change in piezoresistance of the cantilever resulting froman atomic force applied to the cantilever.

An embodiment includes a method of performing atomic force microscopy(AFM) comprising providing a first electrode and a second electrodeengaged to a substrate and providing a branched cantilever wherein thecantilever comprises a nanostruture. Next, the method discloses engaginga first arm of the cantilever to the first electrode and a second arm ofthe cantilever to the second electrode. Furthermore, the methodcomprises positioning the cantilever adjacent to a substance to beanalyzed and measuring a change in a piezoresistance of the cantileverresulting from an atomic force acting upon the cantilever by thesubstance to be analyzed.

In an embodiment, a cantilever probe comprises a first electrode and asecond electrode engaged to a substrate and a branched cantileverwherein the cantilever comprises a nanostruture. In an embodiment, aprobe comprises a first arm of the cantilever engaged to the firstelectrode and a second arm of the cantilever engaged to the secondelectrode and a ferromagnetic material engaged the cantilever.Additionally, an electrical circuit coupled to the cantilever whereinthe electrical circuit is capable of measuring a change inpiezoresistance of the cantilever resulting from a magnetic forceapplied to the cantilever.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be further explained with reference to theattached drawings, wherein like structures are referred to by likenumerals throughout the several views. The drawings shown are notnecessarily to scale, with emphasis instead generally being placed uponillustrating the principles of the present invention.

FIG. 1 shows a schematic drawing of an analytical device for use in ananoscale MRFM containing the CNT cantilever probe of the invention.

FIG. 2 shows a schematic drawing of an MRFM layout of the analyticaldevice with a CNT cantilever probe.

FIG. 3 shows scanning electron microscope (SEM) photomicrographs ofsymmetrically branched (Y-shaped) CNTs at (a) low magnification (scalebar=1 μm) and (b) high magnification (scale bar=200 nm).

FIG. 4A shows an SEM image of about 100 nm diameter multi-walled CNTsgrown by a chemical vapor deposition process on nanolithographicallyprepared silicon substrates.

FIG. 4B shows an AFM photomicrograph of tungsten wires onsilicon-nitride on a silicon wafer surface.

FIG. 5 shows an embodiment of the invention wherein the cantilever isengaged to a set of electrodes by a device-on-electrode methodology.

FIG. 6 shows an embodiment of the invention wherein the cantilever isengaged to a set of electrodes by an electrode-on-device methodology.

FIG. 7 shows an embodiment of the invention wherein the cantilever isengaged to a set of electrodes by a combination of device-on-electrodeand electrode-on-device methodologies.

FIG. 8 shows an embodiment of a zinc-oxide (ZnO) nanostructure.

While the above-identified drawings set forth preferred embodiments ofthe present invention, other embodiments of the present invention arealso contemplated, as noted in the discussion. This disclosure presentsillustrative embodiments of the present invention by way ofrepresentation and not limitation. Numerous other modifications andembodiments can be devised by those skilled in the art which fall withinthe scope and spirit of the principles of the present invention.

DETAILED DESCRIPTION OF THE INVENTION DEFINITIONS

The term “CVD” refers to chemical vapor deposition. In CVD, gaseousmixtures of chemicals are dissociated at high temperature (for example,CO₂ into C and O₂). This is the “CV” part of CVD. Some of the liberatedmolecules can then be deposited on a nearby substrate (the “D” in CVD),with the rest pumped away.

The term “piezoresistance” is defined in the art as a change inresistance in a material, caused by an applied stress. Piezoresistanceor piezoelectric properties of CNTs are the variations of the electricalresistance of the CNT due to stress caused by a deflection or bending ofat least one end.

The term “ferromagnetic” is afforded the term commonly given in the art.A “ferromagnetic material” is a material having the ability to maintainmagnetization in the absence of a magnetic field. Typical ferromagneticmaterials comprise elements selected from transition metals of theperiodic table and alloys thereof. Preferred ferromagnetic elements arecobalt, iron, nickel, and alloys thereof.

The term “nanomagnet” is defined in the art as a ferromagnetic materialhaving dimensions from about 1 nanometer (nm) to about 10 micrometers.

MRFM Device Comprising a CNT Ferromagnetic Probe

In an embodiment, an MRFM analytical device comprises amicro-dimensional probe that is capable of detecting single proton andsingle electron spin. More specifically, a micro-dimensional probe foran MRFM device comprises a CNT cantilever that includes a ferromagneticparticle. In an embodiment, the CNT cantilever can be attached to anelectrode as a component of a probe. In an embodiment, the probe can becoupled with an electrical circuit as a component of a device fornanoscale MRFM micro-dimensional probes.

FIG. 1 shows an embodiment of a cantilever probe. Two arms of a branchedCNT cantilever 1, are connected to electrodes 3, which are engaged to asurface of a substrate 4. A ferromagnetic material 2 is attached to thecantilevered end of the CNT cantilever 1. Arrows 5 show the direction ofan alternating electrical current flowing though the device. Thegradient field felt by the specimen spins are represented by dashedlines 6.

In an embodiment, the cantilever comprises a nanostructure. In anembodiment, the nanostructure is a CNT. In an embodiment, CNTs arecylinders of networked carbon atoms that can have cylindrical diametersas small as about 0.4 nm (1 mn=10⁻⁹ m). In an embodiment, CNTs can beprepared in lengths from about 10 nm to about 100,000 nm (0.1 mm) anddiameters from about 1 nm to about 100 nm. Those skilled in the art willrecognize that CNTs of various lengths and/or diameters are within thespirit and scope of the present invention.

In an embodiment, smaller diameter CNTs (about 0.4 nm to about 10 nm)may be comprised of a single tubule of networked carbon atoms, and arereferred to as single-walled carbon nanotubes (hereinafter referred toas SWNTs). In an embodiment, CNTs also may comprise nested concentriccylinders, referred to as multiwalled carbon nanotubes (hereinafterreferred to as MWNTs). In an embodiment, the dimensions are a diameterbetween about 1 nm and about 50 nm, and a length between about asubmicron and about 100 micrometers. In an embodiment, the CNT tubuleshave a length ranging between about 1 micrometer to about 10micrometers.

In an embodiment, CNTs have conducting properties depending on chirality(the rotation of the symmetry of carbon network along the cylinderaxis). In an embodiment, CNTs can be metallic, semiconducting orinsulating. In an embodiment, single walled nanotubes can be metallic orsemiconducting, depending on chirality. In an embodiment, MWNTs aremetallic. Both CNT species are mechanically robust, with a Young'smodulus of about 1 TPa (10¹² Pa). Those skilled in the art willrecognize that CNTs with a wide range of Young's modulus values arewithin the spirit and scope of the present invention.

The sub-micron diameter makes CNTs ideal candidates for thereduced-size, “nanoscale” cantilevers required for MRFM imaging ofnanoscale features in samples. Moreover, the small dimensions will leadto increased mechanical resonance frequencies due to the smaller mass(resonance frequency varies inversely with the square root of the massf_(o)˜1/m^(1/2)), a beneficial quality for imaging. As an additionalbenefit, CNTs offer significant advantages in that they possesspiezoelectric properties. The piezoelectric properties allow forinternal detection of the movement of a cantilever comprised of a CNT.As such, internal detection of cantilever movement eliminates the needfor an external detection device such as the reflection of a laser beamoff the cantilever toward a photodiode detector. In addition, CNTs alsopossess substantially higher strength-to-weight ratio and superiormechanical properties over other materials such as silicon.

CNTs can be linear or non-linear. “Linear CNTs” as defined herein, referto CNTs that do not contain any branches originating from the surface ofindividual CNT tubules along their linear axes. “Branched CNTs” asdefined herein, refer to non-linear CNTs with at least one locationalong the linear tubule axis or at the tubule terminal from which one ormore tubules originate, having linear tubule axes that are non-identicalto the tubule from which they originate. Such points of origination ofadditional tubules (branch points) are also referred to herein as“junctions”. In an embodiment, the branched CNT is Y-shaped. In anembodiment, the branched CNT is V-shaped. In an embodiment, the branchedCNT is T-shaped. In an embodiment, the branched CNT is X-shaped. Thoseskilled in the art will recognize that various other morphologies and/orconfigurations are within the spirit and scope of the present invention.

In an embodiment, the individual arms constituting branched tubules areeither symmetrical or unsymmetrical with respect to both arm lengths andthe angle between adjacent arms. In an embodiment, each individual armis between about 1 nm and about 100 micrometers in length. Those skilledin the art will recognize that a wide range of lengths of arms and awide rang of angles between adjacent arms are within the spirit andscope of the present invention.

FIG. 3 shows an image of an embodiment of a Y-shaped CNT. In anembodiment, the Y-shaped CNTs exist as (1) a plurality of free standing,branched CNTs attached to the substrate and extending outwardly from thesubstrate outer surface; and (2) one or more CNTs with a branchedmorphology wherein the CNT tubule structures have Y-junctions withnominally straight tubular arms and nominally fixed angles between saidarms.

In an embodiment, the probe comprises a CNT cantilever which isV-shaped. FIG. 4A shows images of an embodiment of a V-shaped CNT.Important structural attributes of CNTs that determine their mechanicaland electrical properties can be controlled and “tailored” for specificrequirements.

In an embodiment, a ferromagnetic particle is engaged to an arm of theCNTs. The ferromagnetic particle comprises a ferromagnetic material. Inan embodiment, ferromagnetic materials comprise elements selected fromtransition metals of the periodic table and alloys thereof. In anembodiment, the ferromagnetic particle comprises cobalt, iron, nickel,or alloys thereof. In an embodiment, the ferromagnetic particlecomprises a plurality of ferromagnetic particles. In an embodiment, theferromagnetic particle is in the form of a nanorod. In an embodiment,the nanorod comprises a length of about 10 nm to about 100 nm; in anembodiment, the ratio of the length to diameter of the nanorod is about2 to about 100. Those skilled in the art will recognize that anyferromagnetic particle may be engaged to the disclosed cantilever andremain within the spirit and scope of the present invention.

Cantilever Probe Fabrication

Methods for fabricating an analytical device comprising a CNT cantileverprobe are disclosed. FIG. 1 and FIG. 2 show an embodiment of theassembly of the components comprised in an embodiment of the MRFManalytical device. In an embodiment, the nanotube is positioned asfollows: immobilizing two arms of a Y-shaped cantilever 1 to twoelectrodes 3 on a substrate 4, with the third arm cantilevered out fromthe substrate edge, as depicted in FIG. 1 and FIG. 2. The flow of acharge from a first arm of a cantilever to a second arm of thecantilever is designated by arrows 5. FIG. 2 depicts the full MRFMlayout of the device in which the CNT cantilever 1 is cantilevered outfrom the substrate 4, and a ferromagnetic material 2 is attached to thefree arm of the CNT cantilever 1. The gradient field 6 is felt by samplespins 15. An RF coil is represented as a microcoil 8 integrated into thesubstrate 4 and produces an RF magnetic field 7.

In an embodiment, branched CNT cantilevers are attached to or grown ontolithographically prepared substrates containing surface metalelectrodes. In an embodiment, the substrate comprises on-chip signalprocessing capabilities.

In an embodiment, the Y-shaped CNTs are used as an MRFM cantilever byattaching the ends of the top two arms of the Y to a substrate, with thebottom, third arm cantilevered out over the edge of the substrate. Anembodiment of a Y-shaped CNT is shown in FIG. 3.

In an embodiment, V-shaped CNTs are used as an MRFM cantilever byattaching the arms of the V to a substrate, with the junctioncantilevered out over the edge of the substrate. An embodiment ofV-shaped CNTs are shown in FIG. 4A.

In an embodiment, Y-shaped and V-shaped CNTs are placed on a substrateusing Scanning Probe Microscopy (SPM) manipulation techniques which areknown in the art. In an embodiment, the cantilevered arm protrudesperpendicularly from the substrate. In an embodiment, the cantileveredarm lies parallel to the substrate at a substrate edge, such that thedevice cantilevers out from the edge. Those skilled in the art willrecognize that the cantilevered arm may protrude from the substrate atany angle and remain within the spirit and scope of the presentinvention.

Connection of the CNT cantilever to a substrate, such as for examplesilicon, may be accomplished in the following ways: namely,device-on-electrodes, electrodes-on-device or a combination of bothmethods. FIG. 5 shows an embodiment of the invention wherein thecantilever is engaged to a substrate by a device-on-electrode method.FIG. 6 shows an embodiment wherein the cantilever is engaged to thesubstrate by an electrode-on-device method. FIG. 7 shows an embodimentof the invention wherein the cantilever is engaged to the substrate by acombination of both methods, i.e., a first arm of the cantilever isengaged to the substrate via a device-on-electrode method and a secondarm of the cantilever is engaged to the substrate via anelectron-on-device method.

In device-on-electrodes configuration, metallic lead electrodes aredeposited by conventional lithographic techniques, possibly includingelectron-beam lithography, onto a passivated semiconductor substrate(e.g. silicon dioxide or silicon nitride, on silicon). These electrodesare of appropriate thickness, width, length and proximity for laterattachment of CNT cantilevers. In an embodiment, electrode dimensionshave a thickness of about 100 nm, width of about 100 nm, length of up toabout several millimeters (in an embodiment, length of about 1 mm), andproximity (distance between two planar electrodes) of about 100 nm. Inan embodiment, the substrate may be prepared with vertical void regions,or edges, with the above electrodes deposited to the edges. CNTcantilevers may then be placed onto the substrate, such as by dispersionof CNTs in solution which is then evaporated, and physically manipulatedinto place atop the prepared electrodes. One arm of a Y-shaped CNT orthe joint of a V-shaped cantilever would be cantilevered out over thesubstrate edge, or over the void area, forming a cantilever. In anembodiment, additional electrical contact of the fixed ends of the V- orY-CNT to the surface metallic electrodes could be achieved byelectrodeposition, electroless deposition, or electron beam “welding” ina scanning electron microscope (SEM).

Regarding an electrodes-on-device configuration, as shown in FIG. 6, theCNT cantilever is situated on the substrate prior to metal electrodedeposition. In a similar fashion to the former device-on-electrodesconfiguration, the CNT may be manipulated with an SPM into position,forming a cantilever. In an embodiment, the planar coordinates of thefinal location of the CNT can be identified with an SEM or an SPM. Thesecoordinates are then later used to program a photolithographic orelectron beam lithographic system to accurately place metallicelectrodes onto a surface and overlapping the ends of the fixed portionsof the CNTs, making electrical contact. In an embodiment, preparation ofthe electrodes-on-device configuration involves a Y or V-shaped CNTsituated flat on a substrate. In an embodiment, photolithographictechniques known to the art may be used to both accurately placemetallic electrodes overlapping the ends of the Y or V-shaped CNT, andto etch the substrate so as to remove substrate material below a portionof the CNT, facilitating a cantilevered arrangement.

An advantage of using V-shaped CNTs is the ability to grow the CNTcantilevers directly on the substrate, without the added step ofattaching a pre-formed CNT cantilever to the substrate. In anembodiment, V-shaped carbon nanotube devices can be formed by growingtwo nanotubes in precise, close proximity (typically from about 10 nm toabout 100 nm) using nanoscale electron-beam lithography, and attaching aferromagnetic particle to their juncture. Those skilled in the art willrecognize that various methods of growing V-shaped CNTs are within thespirit and scope of the present invention.

FIG. 4B shows an AFM image of tungsten wires on silicon-nitride on asilicon wafer surface. The bumps visible at the ends of each wire arenickel nanodots situated to serve as catalyst sites for subsequentgrowth of CNTs. Referring to FIG. 4A and FIG. 4B, closely spacednanotubes can be brought into contact electrostatically, and thenattaching, by for example electroless deposition, a ferromagneticnanoparticle to their juncture. The resulting V-shaped device can thenbe excited electromagnetically (Lorentz force) into mechanicalresonance, for MRFM detection.

Nanomagnetic Incorporated CNT Probes

CNTs with pre-determined morphology, such as for example, Y-shaped CNTs,can be synthesized using a variety of methods known in the art.Processes for producing quantities of CNTs having varied morphology,including Y-shaped CNTs, are described in W. Z. Li, et al. AppliedPhysics Letters, Volume 79 (12),2001, Pages 1879-1881, and J. Li, etal.Applied Physics Letters, Volume 75 (3), 1999, Pages 367-369, whichare incorporated herein by reference in their entirety.

As shown in FIG. 3, branched CNTs typically comprise a plurality ofY-junctions with substantially straight arms extending linearly fromsaid junctions. In an embodiment, CNTs possess Y-junctions having twolong arms that are a few microns long (about 2 to about 10 μm), and athird arm that is shorter (about 0.01 to about 2 μm). In an embodiment,the CNTs comprise Y-junctions comprising three long arms (up to about 10μm). In an embodiment, the method of the invention provides CNTscomprising multiple branches which results in multiple Y-junctions withsubstantially linear, straight arms. A high magnification SEM micrograph(FIG. 3B) shows that an embodiment of the branched CNTs possessY-junctions that have a smooth surface and uniform tubule diameter ofabout 200 nm. In an embodiment, the angles between adjacent arms areclose to about 120°, thereby resulting in branched CNTs that have asubstantially symmetric structure. In an embodiment, all Y-junctionshave a substantially similar structural configuration, regardless oftheir varying tubule diameters.

In an embodiment, the CNTs comprised in the probes can be synthesized inaddressable arrays. Fabrication of addressable CNT arrays utilizes bothmicro-and nano-lithographic preparation of CNT catalyst sites andmetallic addressing wires on single crystal silicon wafers.Subsequently, growth of aligned CNTs on the catalyst surface isaccomplished via CVD. In an embodiment, a series of thin gold wires aredefined lithographically on the surface of the silicon wafer, whereinthe inner ends of pairs of individual wires are in close proximity, forexample, about 100 nm apart. In an embodiment, a CNT growth catalyst(for example, nickel (Ni) or cobalt (Co)) nanodot site is defined atthese proximal ends using e-beam lithography, following which thecatalyst material is deposited. In an embodiment, the wafers are thenplaced in a chemical vapor deposition (CVD) chamber to initiate CNTgrowth. In an embodiment, CNT growth occurs at the catalyst nucleationsites.

The fabrication schemes for MRFM probes rely on the use of a nanomagnetsuch as a ferromagnetic material as the field sensor. In an embodiment,a ferromagnetic material can be attached to the branched CNT cantileveron post-synthesis using typical deposition techniques known in the art(e.g., CVD, and electroless deposition). In an embodiment, theferromagnetic material is incorporated onto the CNT cantilever as aresult of in situ nanotube formation.

In an embodiment, the nanomagnet material in the tubule end of the CNTcantilever probes are generated in-situ during the CNT synthesis. In anembodiment, the catalytic material used in the tubule synthesiscomprises a ferromagnetic material that is retained at the tubule endsof the branched CNTs upon synthesis, thereby functioning as “in-situdeposited” nanomagnets in the CNT probe of the invention. In anembodiment, the metal catalysts include the metallic materials,including their mixtures and alloys that have ferromagnetic properties.In an embodiment, transition metals include iron, cobalt and nickel,including mixtures and alloys thereof. In an embodiment, the transitionmetal is cobalt. For the in-situ incorporation of the nanomagnetmaterial on the CNT probes of the invention, the catalytic materialcomprising at least one transition metal or transition metal alloy thatis deposited on or impregnated within a support substrate comprising ametallic material or a non-metallic material, such as for example, anon-metallic oxide as microparticles. In an embodiment, the catalystmicroparticles nucleate the tubule growth in the CNT growth process,whereby they migrate towards the growing ends of the branched CNTtubules and aggregate to form a nanomagnet. The non-metallic oxidecomprising the catalytic substrate can be either a transition or anon-transition metallic oxide, or a non-metallic inorganic oxide.Metallic oxides useful in the catalyst materials include, for example,oxides of beryllium, magnesium, calcium, strontium and barium. Preferredmetallic oxides include magnesium oxide and calcium oxide. In acurrently preferred embodiment, the metallic oxide is magnesium oxide(MgO). In an embodiment, the CNT growth process can be controlled toobtain tubules of approximately uniform dimensions within arrays.Depending on growth conditions (which in turn, are influenced by thecatalyst material), individual tubules in an array can vary in heightbetween about 10% to about 50% in any given growth run. Parameters inthe growth process of the CNT probe component can be varied to includethe separation distance between catalytic sites on the substrate (andtherefore, between tubule pairs, and tubule branches), and the dimension(diameter and height) of the catalyst microparticles that nucleates thetubule growth and the catalyst deposition method thereby providingcontrol over the size of the nanomagnet growth in situ. Control of theCNT growth process can be utilized to obtain CNT probes of the inventioncomprising in-situ generated nanomagnets and multi-walled CNTs withtubule diameters that are controllable down to about 100 nm. In anembodiment, CNT probes with smaller tubule sizes can be obtained byusing aligned CNT arrays of single-walled nanotubes.

In an embodiment, the nanotube structure can be driven into mechanicalresonance with a Lorentz force, obtained with the use of a staticpolarizing field oriented in the plane of the “Y” or “V”, crossed by analternating current passing through the two anchored arms of thestructure, as in FIG. 2. A ferromagnetic material engaged to the CNTcantilever serves as both the generator of a strong magnetic fieldgradient to be felt by the spin system to be analyzed (see, for example,FIG. 2), and as the active magnetic sensor which feels the reactionforce applied by this spin system. In the usual SPM manner, this MRFMdetector can be x-y-z scanned to facilitate 3D imaging of the sample.

In an embodiment, the two fixed arms of the branched CNT cantilever maybe attached to metallic electrodes, and an electric current can be sentinto one arm and out the other, as in FIG. 1. In an embodiment, as thecantilevered end of the branched assembly moves under the influence ofmagnetic forces, a strain-induced change in the electrical resistance ofthe assembly is measured.

In an embodiment, the shape of the branched CNT structures facilitatesdirect electrical resistance measurements, with nanotube cantileverdeflection causing resistance changes via the piezoresistance effect,measured through the attached arms of the branched CNT cantilever.

The conducting, and piezoconducting, properties of these multi-walledCNTs are sensitive to defects, over which there is some degree ofcontrol in the growing stage. In an embodiment, the defect sensitivitycan be beneficial. In addition to piezoresistance, the branched CNT canexhibit nonlinear rectifying characteristics, such as for example, in adiode, such that the strain dependent conductivity of the nanotube canbe incorporated into a nanoscale amplifying circuit such as for example,a FET, dramatically enhancing the sensitivity to motion. Diodic behaviorat room temperature is observed by both STM studies and direct transportacross large arrays. Thus, in addition to using piezoresistance todetect the branched CNT cantilever motion, a related detection methodcould integrate the structure into a nanoelectronic transistor circuit,with potential for significant gains in sensitivity.

Nanoscale Scanned Probe Microscopy

In an embodiment, the cantilever probe may be utilized in performingvarious other types of “scanned probe microscopy” (SPM). In anembodiment, the cantilever is used in atomic force microscopy (AFM).

An embodiment includes an improved method of performing AFM; morespecifically, an embodiment provides a method of performing AFM whereinthe improvements are in planar spatial resolution, vertical spatialresolution and sensitivity, and data acquisition speed. Suchimprovements are a result of the nanoscale size of the cantilever probe.

In an embodiment, a y-shaped CNT is utilized to perform AFM. In anembodiment, a first arm of the y-shaped CNT 1 and a second arm of they-shaped CNT 1 are engaged to a substrate 4. In an embodiment, a thirdarm of the Y-shaped CNT 1 extends out from the substrate. In anembodiment, the third arm of the Y-shaped CNT 1 does not comprise amagnetic tip. In an embodiment, an electric current is passed betweenthe first arm and the second arm, and the current is measured. Due tointrinsic piezoresistivity, a voltage-to-current ratio (resistance) willchange when the cantilever deflects as a result of the free branchexperiencing atomic force interaction with atoms on the surface of theobject being analyzed.

Due to the nanoscale size of the cantilever, especially the diameter,the spatial resolution of AFM can be improved with this technique. Dueto the significantly smaller total mass of the cantilever probe, ascompared to that of a conventional silicon cantilever, the minimumresponse time (or data acquisition time) for an AFM image can be greatlyimproved (i.e. decreased). This is because the response time varies asthe square root of the mass, following Hooke's law.

In addition, use of the AFM cantilever may improve AFM sensitivity,measured as the minimum detectable vertical deflection of the cantileverdue to an atomic force interaction with a surface. In conventional AFMdevices, imaging sensitivity is limited by such parameters as themechanics of the cantilever, the absolute temperature, the acousticenvironment of the apparatus, the shot noise in the photodiode, andother considerations. Thus, while theoretical limits to spatial(vertical) resolution can be shown to be of the order of about 10⁻⁵ nm,the practical limit is closer to the range of about 0.1 nm to about 0.01nm. While the AFM cantilever may be limited by many of these sameparameters (except those relating to optics, i.e. laser and photodiode),the AFM cantilever does show an improvement over prior art cantilevers.With use of the AFM cantilever of the present invention, a resistancechange corresponding to at least about 10⁻³ nm may be resolved.

FIG. 5, FIG. 6 and FIG. 7 show an embodiment of the AFM cantilever 1.The only difference between the above-identified figures is the methodof engaging the first arm of the cantilever and the second arm of thecantilever to a substrate (discussed above). As shown in FIG. 5, a firstelectrode 3 and a second electrode 3 are engaged to a substrate 4. In anembodiment, a first arm of the AFM cantilever 1 is engaged to the firstelectrode 3 and a second arm of the AFM cantilever 1 is engaged to asecond electrode. In an embodiment, a third arm projects out from thesubstrate. In an embodiment, the third arm does not comprise a magneticmaterial. In an embodiment, a charge is delivered from the first armengaged to the second arm (arrows 5 in FIG. 5 show the flow of thecharge.) In an embodiment, any change in the charge between the firstarm and the second arm may be detected by similar means as discussedabove.

Various forms of AFM may be performed with the AFM cantilever. In anembodiment, the method comprises performing contact AFM. In anembodiment, the method comprises performing noncontact AFM. In anembodiment, the method comprises performing intermittent contact AFM. Inan embodiment, the method comprises performing Lateral Force Microscopy(LFM). In an embodiment, the method comprises performing Atomic ForceAcoustic Microscopy (AFAM). In an embodiment, the method comprisesperforming Spreading Resistance Imaging (SRI). In an embodiment, themethod comprises performing AFAM Resonance Spectroscopy. In anembodiment, the method comprises performing Electric Force Microscopy(EFM). In an embodiment, the method comprises performing ScanningCapacitance Microscopy (SCM). In an embodiment, the method comprisesperforming Kelvin Probe Microscopy (KPM or SKM). In an embodiment, themethod comprises performing Dissipation Force Microscopy (DFM). Thoseskilled in the art will recognize that various other forms of AFM arewithin the spirit and scope of the present invention.

Cantilever Probes Comprising Non-Carbon Materials

Various embodiments of cantilever probes used in various forms ofmicroscopy, such as MFM, MRFM and AFM are herein disclosed. As discussedabove, the cantilevers may comprise nanostructures comprised of carbon.In an embodiment, the cantilevers may comprise non-carbonnanostructures.

In an embodiment, the cantilever is piezoresistive. In an embodiment,the cantilever is intrinsically piezoresistive. In an embodiment, thecantilever is extrinsically piezoresistive. By “intrinsicallypiezoresistive” it is meant that the cantilever exhibitspiezoresistivity. By “extrinsically piezoresistive” it is meant that thecantilever exhibits piezoresistance after being processed in such a wayas to induce piezoresistivity or is coated with a piezoresistivematerial in order to render the cantilever piezoresistive.

As such, in an embodiment, the cantilever comprises non-carbonnanostructures. In an embodiment, the non-carbon nanostructures exhibitpiezoresistivity. In an embodiment, a piezoresistive material is engagedto the non-carbon nanostructure.

In an embodiment, the non-carbon material is zinc oxide (ZnO). FIG. 8shows a cantilever probe 1 comprises ZnO. ZnO is known to bepiezoelectric and piezoresistive. In an embodiment, the non-carbonmaterial is silicon. In an embodiment, the non-carbon material isboron-nitride (BN). In an embodiment, the non-carbon material isboron-carbide. Those skilled in the art will recognize that non-carbonmaterial may comprise various materials and semiconductors and remainwithin the spirit and scope of the present invention.

Nanostructures

Various embodiments of cantilever probes are herein disclosed;furthermore, various embodiments disclose the use of such cantileverprobes in procedures such as MFM, MRFM and AFM. As discussed above, thecantilevers may comprise nanostructures. In an embodiment, thenanostructure is a nanotube. In an embodiment, the nanostructure is ananowire. In an embodiment, the nanostructure is a filled tube.

In an embodiment, the nanostrucutres are tubular cylinders and may bedesignated as nanotubes. In an embodiment, the nanostructures comprise amixture of crystalline and amorphous carbon. Such structures may bedesignated nanotubes or nanofibers. In an embodiment, the nanostructureis a nanostalk. In an embodiment, the nanostructures are non-hollow.Those skilled in the art will recognize that various nanostructures arewithin the spirit and scope of the present invention.

Use of Electron Beam Welding to Provide a Desired Cantilever Morphology

In an embodiment, a method discloses the production of bridged ormultiple connected nanostructures such as a Y-shaped, T-shaped, orX-shaped cantilever by a process called electron beam welding. In anembodiment, electron beam welding is performed by arranging a firstnanostructure to come into contact with a second nanostructure. Next, anelectron beam in an electron microscope is used to engage the firstnanostructure with the second nanostructure by focusing the electronbeam on a desired junction point for a period of time sufficient todeposit enough of an amount of an amorphous carbon (unavoidablyavailable in the microscope chamber) to make a mechanical connection.This mechanical connection is usually conducting enough to allowelectrical current to pass from a first branch to a second branch. Assuch, any linear nanostructure can be possibly connected to another,forming a desired cantilever.

The embodiments disclosed herein have several advantages. In anembodiment, the invention directly overcomes one of the maindisadvantages to observation at the molecular level using cantilevers,that of output signal. In an embodiment, the method uses piezoelectricor piezoresistive detection with CNT cantilevers, thereby eliminatingthe need for laser interferometry or mirrored-light detection asrequired by silicon-based cantilevers. CNTs are known in the art to behigh strength, mechanically robust, flexible conducting materials. In anembodiment, the use of CNTs as cantilevers in place of silicon-basedcantilevers in MRFM, improves the state-of-the-art technology frommicrometer-scale resolution by orders of magnitude to nanometer-scaleresolution. In an embodiment, nanotubes improve sensitivity and spatialresolution up to about 1,000 times more than possible with silicon-basedcantilevers. CNT cantilevers are compatible with conventionaltechnologies for fabricating electrically conducting nanocircuits, suchas etched trenches in silicon or surface deposition of thick nanowirecontacts. In an embodiment, nanotube cantilevers can be used ininconvenient environments such as biological media. The discloseddevices have the capability of being built in array form, allowingreal-time, correlative spectroscopy and imaging. Spatially andtemporally correlated detection, in the spirit of functional MRI arepossible. The cantilever probe is a unique and enabling technology thathas the revolutionary capability to fabricate arrays of ultra-sensitiveMRFM devices that can be used for fast imaging. The various embodimentsadvance the measurement capabilities of magnetic detection by reducingthe size of the measurement tools to the nanoscale. Instead ofmicromachining silicon down to the appropriate size, the embodimentsdisclose the use of nanostructures.

The embodiments provide new technologies for constructing MFM, MRFM, andAFM instruments that outperform the current generation of instruments byseveral orders of magnitude in sensitivity and resolution.

The devices of the invention, including mechanical and chemicalprocesses for their preparation, as well as methods for theirfabrication will become apparent to one familiar in the art based on theaforementioned embodiments and the following non-limiting examples.

EXAMPLES Example 1

Preparation of Catalyst Substrate for Synthesis of Linear CNTs

Mesoporous silica containing iron nanoparticles were prepared by asol-gel process by hydrolysis of tetraethoxysilane (TEOS) in thepresence of iron nitrate in aqueous solution following the methoddescribed by Li et al. (Science, (1996), Vol. 274, 1701-3) with thefollowing modification. The catalyst gel was dried to remove excesswater and solvents and calcined for 10 hours at 450° C. and 10⁻² torr togive a silica network with substantially uniform pores containing ironoxide nanoparticles that are distributed within. The catalyst gel isthen ground into a fine, micro-particulate powder either mechanicallyusing a ball mill or manually with a pestle and mortar. The groundcatalyst particles provide particle sizes that range between 0.1 and 100μM under the grinding conditions.

Example 2

Preparation of Catalyst Substrate for Synthesis of Branched CNTs

Catalyst substrates were prepared following the method described by Liet al. (Applied Physics Letters (2001) Vol. 79(12 ),1879-1881).Magnesium oxide (MgO) supported cobalt (Co) catalysts were prepared bydissolving 0.246 g of cobalt nitrate hexahydrate (Co(NO₃)₂.6H₂O, 98%) in40 ml ethyl alcohol, following immersing 2 g of particulate MgO powder(−325 mesh) were added to the solution with sonication for 50 minutes.The solid residue was filtered, dried and calcined at 130° C. for 14hours.

Example 3

General Synthetic Procedure for Branched CNTs

The MgO supported cobalt catalyst of Example 2 were first reduced at1000° C. for 1 hour in a pyrolytic chamber under a flow of a mixturehydrogen (40 sccm) and nitrogen (100 sccm) at a pressure of 200 Torr.The nitrogen gas was subsequently replaced with methane (10 sccm) toinitiate CNT growth. The optimum reaction time for producing branchedCNTs was 1 hour.

Example 4

Characterization of CNT Morphology and Purity by Scanning ElectronMicroscopy (SEM), and Tubule Structure and Diameter by TransmissionElectron Microscopy (TEM)

Scanning electron microscopy (SEM) for characterization and verificationof CNT morphology and purity was performed on a JEOL JSM-6340Fspectrophotometer that was equipped with an energy dispersive x-ray(EDS) accessory. Standard sample preparation and analytical methods wereused for the SEM characterization using a JEOL JSM-6340F microscope. SEMmicrographs of appropriate magnification were obtained to verify tubulemorphology, distribution and purity.

Transmission electron microscopy (TEM) to characterize individual tubulestructure and diameter of the CNTs was performed on a JEOL 2010TEMmicroscope. Sample specimens for TEM analysis were prepared by mildgrinding the CNTs in anhydrous ethanol. A few drops of the groundsuspension were placed on a micro-grid covered with a perforated carbonthin film. Analysis was carried out on a JEOL 2010microscope. TEMmicrographs of appropriate magnification were obtained for determinationof tubule structure and diameter.

Example 5

Controllable Creation of Arrays of Addressable Multi-Walled CarbonNanotubes

CNTs are grown by the plasma-enhanced hot filament chemical vapordeposition method, including on an e-beam patterned substrate. Metallicnickel, deposited via e-beam lithography over a non-catalytic metalprovides the electrical leads, is used as the catalyst for CNT growth.

Example 6

Microdimensional Electrically Addressable Probe Fabrication

Catalyst Deposition on Substrate

The preliminary step in probe fabrication involves a micro- andnanolithographic preparation of CNT catalyst sites and metallicaddressing wires on single crystal silicon wafers. Conventional e-beamevaporation of nickel (Ni) or cobalt (Co) is used after an e-beamlithography step is performed on the substrate to define the catalystsites in an e-beam resist. This is followed by a lift-off step (of theunwanted catalyst material), leaving only the Ni or Co nanodots on topof the gold leads. Alternatively, a self-assembly of catalystnano-particles from a catalyst-containing solution is used, whichprecludes the need for the lift-off step. In either case, at the end ofthis phase, electrically addressable pairs of CNTs with well-definedheights and lateral separations are prepared. Separations betweennanotubes down to 10nm, can be obtained reproducibly by these methods.

Fabrication of Electrically-Addressable Carbon Nanotube Arrays

An array of aligned CNTs are grown on the substrate containing catalyticsites via hot filament, plasma-enhanced chemical vapor deposition(PECVD). A series of thin gold wires lithographically on the silicon isdefined, with the inner ends of pairs of individual wires in very closeproximity (about 100 nm). At these proximal ends, a CNT growth catalyst(for example, Ni or Co) nanodot site is defined using e-beamlithography, and the catalyst material deposited. This wafer is thenplaced in the CVD chamber, with subsequent CNT growth occurring only atthe catalyst nucleation sites. At this point the gold wires may bepassivated using electropolymerization. If deemed necessary, additionalsteps can be introduced to obtain strictly uniform height of the CNTs inthe arrays. Depending on growth conditions used, CNTs height in an arrayin a given growth run can be varied in height by 10%-50%. Heightuniformity is accomplished by performing additional mechanical polishsteps.

All patents, patent applications, and published references cited hereinare hereby incorporated by reference in their entirety. While thisinvention has been particularly shown and described with references topreferred embodiments thereof, it will be understood by those skilled inthe art that various changes in form and details may be made thereinwithout departing from the scope of the invention encompassed by theappended claims.

1. A cantilever probe comprising: a first electrode and a secondelectrode engaged to a substrate; a branched cantilever comprising ananostruture; a first arm of the cantilever engaging the first electrodeand a second arm of the cantilever engaging the second electrode; and anelectrical circuit coupled to the cantilever wherein the electricalcircuit measures a change in piezoresistance of the cantilever resultingfrom an atomic force applied to the cantilever.
 2. The probe of claim 1wherein nanostructure is a nanotube.
 3. The probe of claim 1 wherein thenanostructure is a nanowire.
 4. The probe of claim 1 wherein thenanostructure comprises a crystalline material and an amorphousmaterial.
 5. The probe of claim 1 wherein the nanostructure comprises anon-carbon material.
 6. The probe of claim 5 wherein the non-carbonmaterial is zinc-oxide.
 7. The probe of claim 1 wherein the branchedcantilever is Y-shaped.
 8. The probe of claim 1 wherein the branchedcantilever is V-shaped.
 9. A cantilever probe comprising: a firstelectrode and a second electrode engaged to a substrate; a branchedcantilever comprising a nanostruture; a first arm of the cantileverengaged to the first electrode and a second arm of the cantileverengaged to the second electrode; a ferromagnetic material engaging thecantilever; and an electrical circuit coupled to the cantilever whereinthe electrical circuit measures a change in piezoresistance of thecantilever resulting from a magnetic force applied to the cantilever.10. The probe of claim 9 wherein the nanostructure comprises anon-carbon material.
 11. The probe of claim 9 wherein the nanostructureis a nanowire.
 12. The probe of claim 9 wherein the nanostructurecomprises a crystalline material and an amorphous material.
 13. A methodof performing atomic force microscopy comprising: providing a firstelectrode and a second electrode engaged to a substrate; providing abranched cantilever comprising a nanostruture; engaging a first arm ofthe cantilever to the first electrode and a second arm of the cantileverto the second electrode; positioning the cantilever adjacent to asubstance to be analyzed; and measuring a change in a piezoresistance ofthe cantilever resulting from an atomic force acting upon the cantileverby the substance to be analyzed.
 14. The method of claim 13 whereinnanostructure is a nanotube.
 15. The method of claim 13 wherein thenanostructure is a nanowire.
 16. The method of claim 13 wherein thenanostructure comprises crystalline and amorphous material.
 17. Themethod of claim 13 wherein the nanostructure comprises a non-carbonmaterial.
 18. The method of claim 17 wherein the non-carbon material iszinc-oxide.
 19. The method of claim 13 wherein the branched cantileveris Y-shaped.
 20. The method of claim 13 wherein the branched cantileveris V-shaped.